Most of today's automobiles are equipped with closed-loop, electronic controls supported by on-board microcomputers so as to perform a variety of control functions. Thus, for example, electronic controls are provided to optimize fuel economy and engine operation, meet emission control requirements and to provide for more comfortable and/or safe driving characteristics for the automobile (e.g., such as those characteristics provided by antilocking and/or antiskid braking systems, positive traction systems, suspension adjustment systems and the like). These latter systems are dependant upon the ability of the electronic control loop to sense accurately forces acting upon the automobile system under control and then to exhibit the desired rate-responsiveness in order to exercise adequate control. As more sophisticated electronic control schemes have evolved, it is the sensors which have become performance limiting factors due principally to the inability of sensor fabrication technology to keep pace with the development of integrated automobile control systems.
Recently, however, "micromachining" techniques for forming structural three-dimensional devices from silicon have emerged as a cost-effective means of producing high quality (i.e., sufficiently sensitive) force sensors/transducers useful for the automotive industry. Thus, silicon micromachining techniques have been employed to form force transducers in the form of diaphragms, cantilever beams, microbridges and the like. (See, for example, Lee et al., "Silicon Micromachining Technology For Automotive Applications", SAE Publication No. SP655, February, 1986, the entire content of which is expressly incorporated hereinto by reference.)
It is necessary in many automotive applications (e.g., antiskid braking systems, traction control systems, and the like) for the sensor/transducer to be capable of not only sensing the magnitude of the force acting upon the automobile (i.e., so that the correct amount of control is exercised over the system), but also to be capable of sensing the direction of such forces Conventional force-sensing transducers (i.e., so-called accelerometers which detect acceleration/deceleration forces), and particularly those formed of silicon by micromachining techniques, are typically only capable of sensing forces in one direction. This inability of conventional force-sensing transducers thus necessitates the use of redundant sensors/transducers, each oriented in a particular operative direction in which forces are to be sensed. While such a redundant arrangement may be satisfactory to perform the intended function of providing the control system with force-sensing capabilities in multiple directions, it would obviously be more satisfactory if a single force-sensing transducer was available to sense forces in multiple directions. It is towards attaining such a unitary, multidirectional force-sensing transducer that the present invention is directed.
By way of the present invention, a force-sensing transducer useful in automotive control systems requiring force detection in multiple directions is provided and is preferably embodied in a unitary silicon structure having a planar T-shaped force-sensing body comprised of a base beam and a cantilever beam. Means, such as thin film piezoelectric resistor elements, are provided in operative association with the base and cantilever beams so as to sense respective strains thereof and hence detect forces acting on the body in directions substantially within, and orthogonally to, the plane of the force-sensing body, respectively.
The transducer of the present invention is conveniently fabricated by means of well-known silicon micromachining techniques and thus can be produced economically in fairly small sizes thereby lending themselves for use in a variety of applications, including closed-loop automobile control systems. These and other objects and advantages of this invention will become more clear to the reader after carefully reviewing the detailed description which follows.